SE408326B - CONTROL DEVICE FOR HYDRAULIC SYSTEM - Google Patents

Description

15 20 25 30 35 40 77112654: mediation of hydrostatic transmissions, the working means being a fan and / or one or more brushes. However, other areas are also relevant with regard to the use of hydrostatic transmissions with the possibility of far-reaching control, and only as further examples may be mentioned automatically operating plants for different manufacturing processes, which include working elements, which are kept in motion at different intervals or are continuous in movement but may work at varying speeds depending on the progress of the process.

Regulating the angulation of rocker discs on axial piston-type hydraulic pumps and also regulating the displacement of other types of hydraulic pumps included in conventional hydrostatic transmissions have been solved in many different ways and do not in themselves cause any major problems. It is only when it comes to coordinating the operation of several different hydraulic pumps in a hydraulic system, in which the pumps must be able to cooperate to drive one and the same hydraulic motor and alternatively be able to drive each separate hydraulic motor, that the problems come into play. For large hydraulic systems, there are built-in control systems of a complicated nature, but in the case of smaller hydraulic systems, which are built up of standard components, which are available on the market, and are tailored to a specific purpose, the problems become greater, as there are currently no there is a simple and flexible system available, which can be applied to two or more pumps for alternatively co-operation or selective operation of the hydraulic motors connected thereto in a hydrostatic transmission.

An example of such a smaller hydraulic system is that which occurs in sweepers. In such a machine you have a primary hydraulic pump for operating the machine's castors and one or more secondary hydraulic pumps for operating the fan and / or brush. When the machine is working, it should be driven at a relatively low speed, while it should be possible to drive at a considerably higher speed when transporting from one workplace to another or from the workplace to an emptying point. For economic reasons, the primary pump can not be dimensioned to have sufficient capacity for the higher driving speed, and it is therefore instead made so that it has sufficient capacity for driving at working speed, while it is supplemented with the capacity of the secondary pump or secondary pumps, when driving with 10 l5 20 25 30 35 40 77112654 »transport speed shall be. The requirement is thus that the secondary pumps can be switched from one hydrostatic transmission to another, but also that the capacity of all pumps can be regulated simultaneously from one and the same speed control ("accelerator pedal") without this causing vibrations in the hydrostatic the transmissions, which proved to be difficult to avoid when the control means for different hydraulic pumps in hydrostatic transmissions are interconnected mechanically.

In order to provide a flexible control device of the initially related kind, which allows selective use of the pumps in the hydraulic system, such a control device has obtained the features according to claim 1.

In this way it is achieved that the control device can be built up using standard components and can be adapted to the existing needs and that the control of the operation of the hydraulic pumps can take place without play and vibration. Especially for smaller hydraulic systems, such a control device should be suitable, but there is nothing to prevent it from being used even at larger systems to replace the more inventive built-in control systems that are available for larger systems.

To clarify the invention, an embodiment thereof will be described in more detail in the following with reference to the accompanying drawings.

In the drawings, Fig. 1 is a diagram of a hydraulic system in which the control device according to the invention can be used, while Fig. 2 is a diagram of the control device itself.

The hydraulic system shown in Fig. 1 comprises a shaft 11 coupled to V-belts 10 to an internal combustion engine (not shown), which constitutes a drive shaft for a number of hydraulic pumps for supplying various hydrostatic transmissions with hydraulic fluid under pressure. It can be assumed that in the present case it is a road maintenance vehicle for sucking up waste and pollutants from a road surface and that this vehicle has a mechanical drive transmission 12 to the vehicle's drive wheel, which is coupled to a hydraulic motor 13, and a suction fan 14. , which is connected to a hydraulic motor 15. The hydraulic motor 13 is connected via lines 16A and 16B to a hydraulic pump 17 with variable and reversible flow, for example an axial piston pump with rocker plate, the yoke of which is adjustable for different angles of the rocker plate and thus adjustment of different displacement in one or the other direction of transport 10 15 20 25 30 35 40 77112654: 4 by means of an adjusting arm marked as arrow l8. In the same way, the hydraulic motor 15 is connected via lines 18A and 18B to a hydraulic pump 19 with variable and reversible flow, and also this pump can be constituted by an axial piston pump of the same type as the pump 17. Its adjusting arm is marked with an arrow 20 In addition to the pumps 17 and 19, a hydraulic fluid pump 21 is connected to the drive shaft 11 which is used to provide the required control pressure in the control device according to Fig. 2, as will be described later, and this pump has a pressure line 22 and a suction line 23, the latter is connected to a hydraulic fluid reservoir 24.

The motor 13 and the pump 17 together with the lines 16A and 16B form a hydrostatic transmission between the drive shaft 11 and the mechanical drive transmission 12, while the motor 15 and the pump 19 together with the lines 18A and 18B form a hydrostatic transmission between the drive shaft 11 and the fan 14. However, in In this case, the pump 19 is run parallel to the pump 17, so that both pumps deliver hydraulic fluid to the motor 13, and for this purpose the lines 16A and 18A are connected through a line 25A via a non-return valve 26A and the lines 16B and 18B are connected through a line 25B via a check valve 26B. In addition, a servo valve 27 is arranged in the line 18A, which is normally closed - the position shown - but which, when pressed in its servo line 28, is switched to the open position.

Of course, a hydraulic system of the type shown in Fig. 1 also includes filters, overflow lines, leak oil lines, etc., but these practical details have been omitted here so as not to unnecessarily burden the scheme with those which are not of immediate interest in connection with the invention. .

The following four operating conditions must now be able to be established in the hydraulic system according to Fig. 1, namely: 1. The pump 17 is set to a displacement between 0 and the maximum for operation of the motor 13 in one direction, corresponding to driving forward, while the pump 19 is set to displacement 0.

This means that the fan 14 is stationary and that the vehicle is driven at the desired speed, but not more than the speed corresponding to the capacity of the pump 17. This speed can be described as "slow forward". 2. If the pump 17 is now set to a displacement between 0 and the maximum for operation of the motor l3 in the other direction, the operation of the vehicle "slow reverse" is obtained under the same conditions as in the state l 10 l5 20 25 30 35 40 77112654. With the pump 17 set according to the operating condition 1 above, the pump 19 is set for operating the fan, and this operating condition, in which the vehicle moves "slowly forward" with the fan running, can be referred to as "sweeping". 4. In parallel with the pump 17 being set according to the operating condition 1 above, the pump 19 is set between the displacement 0 and the maximum so as not to supply the motor l5 of the fan 14 but instead the motor 13 with hydraulic fluid, so that this latter motor is supplied with a maximum amount of hydraulic fluid. corresponds to the combined capacity of the two pumps. This operating condition can be called "transport". because it was used to move the cleaning vehicle quickly from one workplace to another or from one workplace to an emptying site.

The control device according to Fig. 2, to which reference is now made, is designed in such a way that with simple operating means the necessary adjustment of the adjusting arms 18 and 20 can be achieved so that a play-free and vibration-free control of the hydraulic pumps is obtained and a smooth transition between the various operating conditions.

Fig. 2 shows the adjusting arms 18 and 20, the pump 21 with the pressure line 22 and the suction line 23, the reservoir 24 for hydraulic fluid and the servo valve 27 with the servo line 28. Thus, it should be easy to understand the functional connection between the hydraulic system in Fig. 1 and the control device in Fig. 2. The control device is of the electrohydraulic type.

To the adjusting arm 18, which is a double-armed lever with a center of oscillation at 30, is connected a tandem cylinder 31 with cylinder chambers 31A and 31B, in which there are pistons 32A and 32B with piston rods 33A and 33B. Thereby, the piston rod 33A is connected to one end of the rack 18, while the piston rod 33B is connected to a fixed anchorage 34. The piston rod sides of the cylinder chambers are connected to the pressure line 22 of the pump 21 through a line 35 to be kept constantly under control pressure.

For the adjusting arm 20, which is a single-armed lever with a center of oscillation at 36, a tandem cylinder 37 is also provided with cylinder chambers 37A and 37B, pistons 38A and 38B and piston rods 39A and 39B.

The piston rod 39A is connected to the actuator arm 20, while the piston rod 39B is connected to a fixed anchor 40, and even in this case the two cylinder chambers on the piston rod side are constantly under control pressure by being connected to the line 35.

The cylinder space 31A is connected via a line 41A on its piston rod opposite piston side partly via a solenoid valve 42A connected to the pressure line 22 for control pressure and partly via a solenoid valve 43A connected to the reservoir 24 through a line 44. Similarly, the cylinder space 31b on its piston rod opposite piston side is connected to the pressure line 22 via a solenoid valve 42B and to the reservoir 24 via a solenoid valve 43B and the line 44.

All of these valves are shut-off valves, as shown by the valve symbols, and they are closed in the de-energized state, which is the state shown.

The cylinder space 37A is connected in the same way as the two cylinder spaces of the tandem cylinder 31 to the pressure line 22 and to the reservoir 24. Since the arrangement corresponds to that of the cylinder space 31A and the valves of the cylinder space 37A in one of the operating states are connected in parallel with the valves 42A and 43A, the line from the cylinder space 37A is denoted by 41A ', while the valve for connecting this line to the pressure line 22 has been denoted by 42A' and the valve for connecting to the reservoir 24 has been denoted by 43A '. These two latter valves are also pure shut-off valves and are shown in the closed, de-energized state.

A line 45 goes to the cylinder space 37B, and this is connectable via a reversing valve 46 alternatively to the pressure line 22 and to the reservoir 24 via the line 44, and the servo line 28 for the servo valve 27 is connected to the line 45.

The valve 46 is a manually operable valve, and a lever 47 is provided for the operation thereof. The valve is displayed in the unaffected state.

The electrical system for operating the servo valves comprises a live wire 50, to which are connected two microswitches 51A and 51b in a feedback mechanism, to be described in more detail, a movable contact 52C in a manually adjustable switch 52 and a movable contact 53C in a manually adjustable switch 53. Movable contacts 52A and 53A and 52B and 53B in the switches 52 and 53 are connected to the line 50 via the microswitches 51A resp. 5lB. The switch 52 is in the position shown, designated I, in the operating states 1-3 as above and is switched to its second position II only for switching on the operating state 4. The switch 53 is a front / reverse switch and is in the position shown I for driving forward in operating states 1, 3 and 4 and in the second position, denoted II. in the operating state 2. A block must be arranged between the switches, so that not both can be in position II at the same time, as will be understood in connection with the function description.

The return mechanism mentioned in passing above comprises a movable housing 54, in which the fixed contacts of the microswitches 51A and 51B are arranged, and this housing is movable in the vertical direction, seen in Fig. 2. It is loaded at the lower end with a pull spring 55, while the upper end is connected via a sliding cable 56 or the like to a pivot arm 57, which has its pivot center at 58. From the pivot arm, the sliding cable branches into two branches 56A and 56B, which are connected to the adjusting arm 18 on either side of its control center 30. A control 59, which may be referred to as an "accelerator pedal", is pivotally mounted at 60 and is normally held by a spring 61 in the position shown against a stop 62. The control has an arm 63 for alternating engagement with the microswitches 51A and 51B variable contacts in the manner to be described.

Regardless of whether the microswitches 51A and 51B are turned on or off, the solenoid valve 42A 'receives power via the connector 52C and also the solenoid valve 42B via the connector 53C, when the switches 52 and 53 are in the positions shown. The valves of the valve solenoids to the other pole on the power source (earth lines) are not drawn, so that the diagram does not become confusing. Assuming that the other valves are not actuated and for a moment look at the condition of the hydraulic system under these conditions, as this is the starting point for the functional description given below, it can be stated that the cylinder chamber 3lB has control pressure on both sides of the piston, the valve 42B is current-carrying and thus in the open position, and that the same is the ratio in the cylinder space 37A, since the valve 42A 'is also current-carrying in the open position. 38A to assume the shown end positions, in which the respective pistons will be locked, as long as the switches 52 and 53 are in position I. As long as the valve 46 is unaffected, i.e. is in the position shown by the symbol, the piston 38B is in the shown left position under the influence of the regulating pressure on the piston rod side in the cylinder space 37B, since this cylinder space on the opposite side is connected to the reservoir 24 via the valve 46. The piston 32A is in the position shown, when the accelerator pedal 59 is unaffected, and is locked in this position, since the two valves 42A and 43A are closed and the piston rod side of the piston 32A is under control pressure. In the various operating states, the position of the piston 32A then becomes dependent on the position of the accelerator pedal.

We shall now consider in turn what happens in the four operating conditions stated above, assuming that the positions shown by the actuators 18 and 20 correspond to the displacement zero of the two pumps 17 and 19; neither the motor 13 nor the motor l5 is running, which means that the vehicle and the fan are stationary.

Operating condition l In this operating condition the vehicle must be driven slowly, - and with the above-mentioned operating condition as a starting point, the accelerator pedal 59 is now depressed, the arm 63 influencing the movable contact of the microswitch 51A, so that this microswitch is closed. This means that the valve 42A now becomes current via the switch 53A of the switch 53 in position I and is brought to the open position, so that control pressure from the pressure line 22 is supplied to the cylinder space 31A on the piston rod opposite the side of the piston. Since this side of the piston has a larger area than the piston rod side of the piston, the piston 32A will be displaced to the left with respect to Fig. 2, the adjusting arm 18 being pivoted counterclockwise about its center of oscillation 30.

By conveying the sliding cable 56 and its branch 56A and while simultaneously swinging the pivot arm 57 counterclockwise, the housing 54 is now lifted in the return mechanism, which means that after some pivoting movement of the actuator arm 18A, the microswitch 51A is brought back to the off position by lifting its fixed contacts moving contact. When the microswitch 51A enters the off position, the valve 42A becomes de-energized again, and thus this valve will be closed, so that the piston 32A is locked in a displacement position corresponding to the current of the accelerator pedal 59 in the cylinder space 31A.

Thus, by the return mechanism, the piston 32A in this operating state will assume a position in the cylinder space 31A, which always corresponds to the current position of the accelerator pedal 59.

If the accelerator pedal 59 is released, it will be swung clockwise under the action of the spring 61 so that the arm 65 will affect the movable contact of the microswitch 51b and this microswitch will be turned on. Thereby, the valve 43A receives current l0 15 20 25 30 35 40 77112654: 9 via the movable contact 53B of the switch 53 in position I, so that the cylinder space 31A on the piston rod opposite the side of the piston is connected to the reservoir 24 through the line 44. The constant pressure control on the piston rod side of the piston 32A is now able to displace the piston 32A to the right, and in an analogous manner as previously described, this will cause the housing 54 to be displaced downwards under the action of the spring 55, so that the microswitch 51b after a certain movement of the housing 54 , will again be switched off with the consequence that the valve 43A becomes de-energized and that the piston 32A is now locked again in the position corresponding to the new setting position of the accelerator pedal 59.

In this operating state, the tandem cylinder 37 is always in the position shown, when it is assumed that the lever 47 has not been actuated and that no changeover of the switch 52 has taken place.

Operating state 2 To achieve this operating state, the switch 53 is actuated from position I to position II. This means that the valve 43B will be opened via the contact 53A in the position II instead of the valve 42A, when the accelerator pedal 59 is depressed, and that the valve 42B, which was previously kept open via the contact 53C in the position I, will be opened via the contact 53B in the position II instead of the valve 43A, when releasing the accelerator pedal. On the other hand, the valve 43A is now in the open position independent of the return mechanism in that it is connected via the contact 53C in the position II to the inlet 50. The return mechanism operates in a manner analogous to that previously described, but as will be appreciated it is now the piston 325 which comes to follow the movement of the accelerator pedal 59 in the same manner as previously described by regulating the pressure on either side of the piston 32B depending on the valves 42B and 43B. Thereby, the adjusting arm 18 is set in a clockwise direction when depressing the accelerator pedal 59 and acts on the return mechanism over the branch 56B of the sliding cable 56. Clockwise rotation of the actuator arm is assumed to correspond to operation of the motor l3 for reverse travel.

Also in this case, the cylinder 37 is assumed to be in the position shown.

Operating state 3 In this operating state, the vehicle can be driven slowly forwards or backwards by actuating the accelerator pedal 59 in the manner described above with respect to operating states 1 and 2. In the operating state 3, however, the lever 47 is manually actuated to change position. Valve 46 from the position shown to the second position, in which the cylinder space 37B on the piston rod opposite the piston is connected to the pressure line 22 instead of being connected to the reservoir 24 through the line 44 as before. carries that the pressure in the cylinder space 37B on the side of the piston rod facing away from the piston rod takes over the control pressure applied to the piston rod side, so that the tandem cylinder 37 is displaced to the left during pivoting of the actuator arm 20 counterclockwise.

At the same time as this occurs, the servo line 28 is also pressurized, so that the valve 27 is switched from its closed position to its open position. We shall now return for a moment to Fig. 1 to see what these control movements mean.

It is assumed that the actuator arm 20, when turned counterclockwise, provides flow through the hydrostatic transmission 15, 18A, 18B, 19 in such a direction that hydraulic fluid can not be transferred via the valves 26A and 26B to the hydrostatic transmission with the motor 13 and the pump 17, i.e. clockwise direction according to Fig. 1. Hydraulic fluid under pressure is thus now circulated through the motor 15 via the open servo valve 27, so that the fan 14 is kept in operation. The fan will be kept in operation regardless of whether the accelerator pedal 59 or the switch 53 is actuated, since the part of the control system which with the switch 52 in the position shown in I shows the setting of the cylinder 31, in no way affects the setting of the cylinder 37.

Operating State 4 As has been apparent from the description of the three operating states above, either pump 17 alone or both pump 17 and pump 19 are used separately in these operating states. In the operating state 4, however, the pump 19 must now operate in parallel with the pump 17 for operating the motor 13.

After the lever 47 has been actuated to return the valve 46 to the position shown, meaning that the cylinder 37 is adjusted so that the motor 15 and thus the fan 14 is stopped, the switch 52 is now actuated to the position II, which, as mentioned earlier, can only take place with the switch 53 in position I. The conversion of switch 52 to position II means that the valves 42A 'and 43A' are connected in parallel with the valves 42A and 43A belonging to the cylinder 31. Therefore, when the piston 32A is adjusted in dependence on the position of the accelerator pedal 59 for pivoting the adjusting arm 18 in the counterclockwise direction and thus driving the vehicle forward, the valves 42A 'and 43A' will also be adjusted to adjust the position of the piston 38A in position Depending on the accelerator pedal 59 during pivoting of the actuator arm 20 in a clockwise direction. On the other hand, since it was assumed above that the direction of supply of the pump 19 when pivoting the actuator arm 20 counterclockwise was such that hydraulic fluid could not pass past the check valves 26A and 26B between the circulation systems of the two pumps 17 and 19, the supply direction now becomes transfer of hydraulic fluid can take place, meaning that the hydraulic fluid transported by the pump 19 through the line 25B goes from the line 18B to the line 16B in Fig. 1 via the non-return valve 26B and after passing the motor 13 returns to the pump 19 through the lines 16A, 25A and 18A via the check valve 26A.

The capacity of both pumps 17 and 19 is thus used for operation of the motor 13, so that it can be driven at high speed in the forward direction.

As mentioned above, there should be a block between switches 52 and 53 to prevent switch 53 from being set to position II while switch 52 is in position II. As will be appreciated from the description of the operating state 4 above, setting the switch 53 in the position II, when the switch 52 is also in the position II, would cause the pumps 17 and 19 to counteract each other. The design described above is special for a road maintenance vehicle and it can be varied in many ways for adaptation to different types of hydraulic systems. The control device can be expanded to control additional hydraulic pumps, which are connected to the drive shaft 11 of the hydraulic system, whereby the pumps can be controlled simultaneously with each other, as takes place in the operating condition 4 as above, or can be switched on and off depending on different switching means in the control device.

Instead of the tandem cylinders 31 and 37 shown, two-stage cylinders can be used, which operate in an analogous manner with a constant control pressure and two adjustable control pressures, as well as the tandem cylinders. The constant control pressure or back pressure, which in the present case is applied to the tandem cylinders through the line 35, can be replaced with springs in the cylinders, but a rigid system with the least possible suspension is obtained, if hydraulic pressure is used as described here. It is also possible to let the tandem cylinders work with compressed air instead of hydraulic fluid, and the electrical system in the control device can be replaced with a fluidistor system.

Claims (5)

10 15 20 25 30 35 40 77112654: 12 _ PATENTKRAV 1. 1. Control device for hydraulic system with a reversible and in at least one direction of transport variable primary hydraulic pump (17) and at least one reversible and in at least one direction of transport variable secondary hydraulic pump (19), wherein the control means (18; 20) of the pumps ) are provided with hydraulic or pneumatic actuating cylinders (31, 37), characterized in that the K actuating cylinders (31, 37) are tandem cylinders or the like and that valves (42A, 42B, 43A; 42A ', 43A', 46 ) are provided for locking one piston (32B; 38B) in the tandem cylinders and adjusting the other piston (32A; 38A) for setting the assigned control means in one direction of travel from a zero position. Control device according to claim 1, characterized in that the valves (42A, 43A; 42A ', 43A') for adjusting said second piston (32B; 38A) are connected to an actuator (59) with feedback (54, 56 ) from the control means (18) of the primary pump (17) for setting this control means in a position corresponding to the current setting position of the actuator. Control device according to Claim 2, characterized in that an electromechanical feedback mechanism is provided for the feedback, comprising switches (51A, 51B) which can be actuated by means of the actuator (59) for controlling the valves (42A, 43A) for adjusting the said second piston (32A) in the tandem cylinder (31) of the primary pump (17) and a mechanical connection (54, 56) between the control means (18) of the primary pump (17) and the switches for canceling the action thereof in the case of predetermined correspondence between the actuator position and position of the regulator. Control device according to any one of claims 1 - 3, characterized in that the valves (42A, 43A) for adjusting said second piston (32A) in the tandem cylinder (31) of the primary pump (17) by means of a switch (53) are connectable to the actuator (59) alternatively with valves (42B, 43B) for adjusting said one piston (32B) in the tandem cylinder of the primary pump for adjusting the control means (18) of the primary pump or alternatively in one or the other conveying direction. Control device according to claim 4, characterized by a switch (52) for switching on and off the valves (42A ', 43A') for adjusting the control means (20) of the secondary pump (19) and a control device 7711265-4 13. (46, 47) for adjusting said one piston (38B) in the tandem cylinder (37) of the secondary pump and thereby adjusting the control means of the secondary pump in the other conveying direction independent of the setting of the primary pump (17). MENTIONED PUBLICATIONS!